Chemistry Semester Exam Review

Which of the following numerical expressions gives the number of moles in 5.0 g of CaO?

• 5.0g x 56 g/mol

• $\frac{5.0g}{56\ g\ mol}$

• $\frac{56\ g\ mol}{5.0\ g}$

• $\frac{1}{5.0g}\times\frac{1}{56\ g\ mol}$

In a lab a student is given a 21 g sample of pure Cu metal. Which of the following pieces of information is most useful for determining the number of Cu atoms in the sample? Assume that the pressure and temperature in the lab are 1.0 atm and 25* C.

• The molar mass of Cu

• The density of Cu at 25 C

• The volume of the Cu sample

• The ratio of the two main isotopes found in pure Cu

A 1.0 mol sample of which of the following compounds has the greatest mass?

• NO

• $NO_2$

• $N_2O$

• $N_2O_5$

The mass spectrum for an unknown element is shown above. According to the information in the spectrum, the atomic mass of the unknown element is closest to

• 90 amu

• 91 amu

• 93 amu

• 94 amu

The mass spectrum represented above is most consistent with which of the following elements?

• Eu

• Gd

• Tb

• Dy

Based on the mass spectrum of a pure element represented above, the average atomic mass of the element is closest to which of the following?

• 185.7 amu

• 186.0 amu

• 186.3 amu

• 186.9 amu

2+(aq)+SO42−(aq)→BaSO4(s)

A student obtains a10.0g sample of a white powder labeled as BaCl2. After completely dissolving the powder in 50.0mL

of distilled water, the student adds excess Na2SO4(s), which causes a precipitate of BaSO4(s) to form, as represented by the equation above. The student filters the BaSO4(s), rinses it, and dries it until its mass is constant. Which of the following scientific questions could best be answered based on the results of the experiment?

• Is the $Na_2SO_4$ (s) used in the experiment pure?
  

• Is the $BaCl_2$ used in the experiment pure?

• What is the molar solubility of $BaCl_2$ in water?

• What is the molar solubility of $BaSO_4$ in water?

A student measures the mass of a sample of a metallic element, M. Then the student heats the sample in air, where it completely reacts to form the compound MO. The student measures the mass of the compound that was formed. Which of the following questions can be answered from the results of the experiment?

• What is the density of M?

• What is the molar mass of M?

• What is the melting point of M?

• What is the melting point of MO?

A42.0g sample of compound containing only C and H was analyzed. The results showed that the sample contained 36.0g of C and 6.0g of H. Which of the following questions about the compound can be answered using the results of the analysis?

• What is the volume of the sample?

• What is the molar mass of the compound?

• What is the chemical stability of the compound?

• What is the empirical formula of the compound?

Mass: 27.3 g

Mass percent of Na: 35.2%

Density: 2.05 g cm-3

Color: white

A jar labeled NaCl contains a powder. The table above contains information determined by analyzing a sample of the powder in the laboratory. What information in the table is the most helpful in determining whether the powder is pure NaCl?

• Mass

• Mass percent of Na

• Density

• Color